Cyclic dimers of alpha hydroxy acids are useful for a variety of applications. For example, lactic acid cyclic dimers, also called lactides, provide an important route to poly(lactic acid). Similarly, cyclic dimers of methionine hydroxy analogs, as described in U.S. Pat. No. 9,011,832, have utility as plasticizers, wetting agents, feed additives, and the like, as well as starting materials for polymers and copolymers comprising heteroatom containing side chains as described in U.S. Pat. No. 9,284,924. Current processes for preparing cyclic dimers of methionine hydroxy analogs, however, have low yields, high capital costs, and large waste streams. Thus, there is a need for improved processes for preparing heteroatom containing cyclic dimers.